Re: [PATCH v3 08/12] KVM: arm64: re-factor hyp.S debug register code

[Christoffer Dall <christoffer.dall@linaro.org>]

On Thu, May 07, 2015 at 10:07:11AM +0100, Alex Bennée wrote:
> This is a pre-cursor to sharing the code with the guest debug support.
> This replaces the big macro that fishes data out of a fixed location
> with a more general helper macro to restore a set of debug registers. It
> uses macro substitution so it can be re-used for debug control and value
> registers. It does however rely on the debug registers being 64 bit
> aligned (as they happen to be in the hyp ABI).


> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> 
> ---
> v3:
>   - return to the patch series
>   - add save and restore targets
>   - change register use and document
> 
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index dfb25a2..ce7b7dd 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -116,6 +116,10 @@ int main(void)
>    DEFINE(VCPU_FAR_EL2,		offsetof(struct kvm_vcpu, arch.fault.far_el2));
>    DEFINE(VCPU_HPFAR_EL2,	offsetof(struct kvm_vcpu, arch.fault.hpfar_el2));
>    DEFINE(VCPU_DEBUG_FLAGS,	offsetof(struct kvm_vcpu, arch.debug_flags));
> +  DEFINE(DEBUG_BCR, 		offsetof(struct kvm_guest_debug_arch, dbg_bcr));
> +  DEFINE(DEBUG_BVR, 		offsetof(struct kvm_guest_debug_arch, dbg_bvr));
> +  DEFINE(DEBUG_WCR, 		offsetof(struct kvm_guest_debug_arch, dbg_wcr));
> +  DEFINE(DEBUG_WVR, 		offsetof(struct kvm_guest_debug_arch, dbg_wvr));
>    DEFINE(VCPU_HCR_EL2,		offsetof(struct kvm_vcpu, arch.hcr_el2));
>    DEFINE(VCPU_MDCR_EL2,	offsetof(struct kvm_vcpu, arch.mdcr_el2));
>    DEFINE(VCPU_IRQ_LINES,	offsetof(struct kvm_vcpu, arch.irq_lines));
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index 15159aa..dd51fb1 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -228,199 +228,52 @@
>  	stp	x24, x25, [x3, #160]
>  .endm
>  
> -.macro save_debug
> -	// x2: base address for cpu context
> -	// x3: tmp register
> -
> -	mrs	x26, id_aa64dfr0_el1
> -	ubfx	x24, x26, #12, #4	// Extract BRPs
> -	ubfx	x25, x26, #20, #4	// Extract WRPs
> -	mov	w26, #15
> -	sub	w24, w26, w24		// How many BPs to skip
> -	sub	w25, w26, w25		// How many WPs to skip
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
> -
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> -1:
> -	mrs	x20, dbgbcr15_el1
> -	mrs	x19, dbgbcr14_el1
> -	mrs	x18, dbgbcr13_el1
> -	mrs	x17, dbgbcr12_el1
> -	mrs	x16, dbgbcr11_el1
> -	mrs	x15, dbgbcr10_el1
> -	mrs	x14, dbgbcr9_el1
> -	mrs	x13, dbgbcr8_el1
> -	mrs	x12, dbgbcr7_el1
> -	mrs	x11, dbgbcr6_el1
> -	mrs	x10, dbgbcr5_el1
> -	mrs	x9, dbgbcr4_el1
> -	mrs	x8, dbgbcr3_el1
> -	mrs	x7, dbgbcr2_el1
> -	mrs	x6, dbgbcr1_el1
> -	mrs	x5, dbgbcr0_el1
> -
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> -
> -1:
> -	str	x20, [x3, #(15 * 8)]
> -	str	x19, [x3, #(14 * 8)]
> -	str	x18, [x3, #(13 * 8)]
> -	str	x17, [x3, #(12 * 8)]
> -	str	x16, [x3, #(11 * 8)]
> -	str	x15, [x3, #(10 * 8)]
> -	str	x14, [x3, #(9 * 8)]
> -	str	x13, [x3, #(8 * 8)]
> -	str	x12, [x3, #(7 * 8)]
> -	str	x11, [x3, #(6 * 8)]
> -	str	x10, [x3, #(5 * 8)]
> -	str	x9, [x3, #(4 * 8)]
> -	str	x8, [x3, #(3 * 8)]
> -	str	x7, [x3, #(2 * 8)]
> -	str	x6, [x3, #(1 * 8)]
> -	str	x5, [x3, #(0 * 8)]
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBVR0_EL1)
> -
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> +.macro save_debug_registers type
> +	// x4: pointer to register set
> +	// x5: number of registers to copy

looking at the caller, you're actually passing the number of registers
to skip?

> +	// x6..x22 trashed
> +
> +	adr	x22, 1f
> +	add	x22, x22, x5, lsl #2
> +	br	x22
>  1:
> -	mrs	x20, dbgbvr15_el1
> -	mrs	x19, dbgbvr14_el1
> -	mrs	x18, dbgbvr13_el1
> -	mrs	x17, dbgbvr12_el1
> -	mrs	x16, dbgbvr11_el1
> -	mrs	x15, dbgbvr10_el1
> -	mrs	x14, dbgbvr9_el1
> -	mrs	x13, dbgbvr8_el1
> -	mrs	x12, dbgbvr7_el1
> -	mrs	x11, dbgbvr6_el1
> -	mrs	x10, dbgbvr5_el1
> -	mrs	x9, dbgbvr4_el1
> -	mrs	x8, dbgbvr3_el1
> -	mrs	x7, dbgbvr2_el1
> -	mrs	x6, dbgbvr1_el1
> -	mrs	x5, dbgbvr0_el1
> -
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> -
> -1:
> -	str	x20, [x3, #(15 * 8)]
> -	str	x19, [x3, #(14 * 8)]
> -	str	x18, [x3, #(13 * 8)]
> -	str	x17, [x3, #(12 * 8)]
> -	str	x16, [x3, #(11 * 8)]
> -	str	x15, [x3, #(10 * 8)]
> -	str	x14, [x3, #(9 * 8)]
> -	str	x13, [x3, #(8 * 8)]
> -	str	x12, [x3, #(7 * 8)]
> -	str	x11, [x3, #(6 * 8)]
> -	str	x10, [x3, #(5 * 8)]
> -	str	x9, [x3, #(4 * 8)]
> -	str	x8, [x3, #(3 * 8)]
> -	str	x7, [x3, #(2 * 8)]
> -	str	x6, [x3, #(1 * 8)]
> -	str	x5, [x3, #(0 * 8)]
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGWCR0_EL1)
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -1:
> -	mrs	x20, dbgwcr15_el1
> -	mrs	x19, dbgwcr14_el1
> -	mrs	x18, dbgwcr13_el1
> -	mrs	x17, dbgwcr12_el1
> -	mrs	x16, dbgwcr11_el1
> -	mrs	x15, dbgwcr10_el1
> -	mrs	x14, dbgwcr9_el1
> -	mrs	x13, dbgwcr8_el1
> -	mrs	x12, dbgwcr7_el1
> -	mrs	x11, dbgwcr6_el1
> -	mrs	x10, dbgwcr5_el1
> -	mrs	x9, dbgwcr4_el1
> -	mrs	x8, dbgwcr3_el1
> -	mrs	x7, dbgwcr2_el1
> -	mrs	x6, dbgwcr1_el1
> -	mrs	x5, dbgwcr0_el1
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -
> +	mrs	x21, \type\()15_el1
> +	mrs	x20, \type\()14_el1
> +	mrs	x19, \type\()13_el1
> +	mrs	x18, \type\()12_el1
> +	mrs	x17, \type\()11_el1
> +	mrs	x16, \type\()10_el1
> +	mrs	x15, \type\()9_el1
> +	mrs	x14, \type\()8_el1
> +	mrs	x13, \type\()7_el1
> +	mrs	x12, \type\()6_el1
> +	mrs	x11, \type\()5_el1
> +	mrs	x10, \type\()4_el1
> +	mrs	x9, \type\()3_el1
> +	mrs	x8, \type\()2_el1
> +	mrs	x7, \type\()1_el1
> +	mrs	x6, \type\()0_el1
> +
> +	adr	x22, 1f
> +	add	x22, x22, x5, lsl #2
> +	br	x22
>  1:
> -	str	x20, [x3, #(15 * 8)]
> -	str	x19, [x3, #(14 * 8)]
> -	str	x18, [x3, #(13 * 8)]
> -	str	x17, [x3, #(12 * 8)]
> -	str	x16, [x3, #(11 * 8)]
> -	str	x15, [x3, #(10 * 8)]
> -	str	x14, [x3, #(9 * 8)]
> -	str	x13, [x3, #(8 * 8)]
> -	str	x12, [x3, #(7 * 8)]
> -	str	x11, [x3, #(6 * 8)]
> -	str	x10, [x3, #(5 * 8)]
> -	str	x9, [x3, #(4 * 8)]
> -	str	x8, [x3, #(3 * 8)]
> -	str	x7, [x3, #(2 * 8)]
> -	str	x6, [x3, #(1 * 8)]
> -	str	x5, [x3, #(0 * 8)]
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGWVR0_EL1)
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -1:
> -	mrs	x20, dbgwvr15_el1
> -	mrs	x19, dbgwvr14_el1
> -	mrs	x18, dbgwvr13_el1
> -	mrs	x17, dbgwvr12_el1
> -	mrs	x16, dbgwvr11_el1
> -	mrs	x15, dbgwvr10_el1
> -	mrs	x14, dbgwvr9_el1
> -	mrs	x13, dbgwvr8_el1
> -	mrs	x12, dbgwvr7_el1
> -	mrs	x11, dbgwvr6_el1
> -	mrs	x10, dbgwvr5_el1
> -	mrs	x9, dbgwvr4_el1
> -	mrs	x8, dbgwvr3_el1
> -	mrs	x7, dbgwvr2_el1
> -	mrs	x6, dbgwvr1_el1
> -	mrs	x5, dbgwvr0_el1
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -
> -1:
> -	str	x20, [x3, #(15 * 8)]
> -	str	x19, [x3, #(14 * 8)]
> -	str	x18, [x3, #(13 * 8)]
> -	str	x17, [x3, #(12 * 8)]
> -	str	x16, [x3, #(11 * 8)]
> -	str	x15, [x3, #(10 * 8)]
> -	str	x14, [x3, #(9 * 8)]
> -	str	x13, [x3, #(8 * 8)]
> -	str	x12, [x3, #(7 * 8)]
> -	str	x11, [x3, #(6 * 8)]
> -	str	x10, [x3, #(5 * 8)]
> -	str	x9, [x3, #(4 * 8)]
> -	str	x8, [x3, #(3 * 8)]
> -	str	x7, [x3, #(2 * 8)]
> -	str	x6, [x3, #(1 * 8)]
> -	str	x5, [x3, #(0 * 8)]
> -
> -	mrs	x21, mdccint_el1
> -	str	x21, [x2, #CPU_SYSREG_OFFSET(MDCCINT_EL1)]
> +	str	x21, [x4, #(15 * 8)]
> +	str	x20, [x4, #(14 * 8)]
> +	str	x19, [x4, #(13 * 8)]
> +	str	x18, [x4, #(12 * 8)]
> +	str	x17, [x4, #(11 * 8)]
> +	str	x16, [x4, #(10 * 8)]
> +	str	x15, [x4, #(9 * 8)]
> +	str	x14, [x4, #(8 * 8)]
> +	str	x13, [x4, #(7 * 8)]
> +	str	x12, [x4, #(6 * 8)]
> +	str	x11, [x4, #(5 * 8)]
> +	str	x10, [x4, #(4 * 8)]
> +	str	x9, [x4, #(3 * 8)]
> +	str	x8, [x4, #(2 * 8)]
> +	str	x7, [x4, #(1 * 8)]
> +	str	x6, [x4, #(0 * 8)]
>  .endm
>  
>  .macro restore_sysregs
> @@ -465,195 +318,52 @@
>  	msr	mdscr_el1,	x25
>  .endm
>  
> -.macro restore_debug
> -	// x2: base address for cpu context
> -	// x3: tmp register
> -
> -	mrs	x26, id_aa64dfr0_el1
> -	ubfx	x24, x26, #12, #4	// Extract BRPs
> -	ubfx	x25, x26, #20, #4	// Extract WRPs
> -	mov	w26, #15
> -	sub	w24, w26, w24		// How many BPs to skip
> -	sub	w25, w26, w25		// How many WPs to skip
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
> +.macro setup_debug_registers type

why introduce a new naming scheme and not just stick to
restore_debug_registers?

the way all this code is written it's:
save: read stuff from HW and *save* it in memory
restore: *restore* stuff from memory and write it to HW

> +        // x4: pointer to register set
> +        // x5: number of registers to copy

ditto: skip/copy

> +	// x6..x22 trashed
>  
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> -1:
> -	ldr	x20, [x3, #(15 * 8)]
> -	ldr	x19, [x3, #(14 * 8)]
> -	ldr	x18, [x3, #(13 * 8)]
> -	ldr	x17, [x3, #(12 * 8)]
> -	ldr	x16, [x3, #(11 * 8)]
> -	ldr	x15, [x3, #(10 * 8)]
> -	ldr	x14, [x3, #(9 * 8)]
> -	ldr	x13, [x3, #(8 * 8)]
> -	ldr	x12, [x3, #(7 * 8)]
> -	ldr	x11, [x3, #(6 * 8)]
> -	ldr	x10, [x3, #(5 * 8)]
> -	ldr	x9, [x3, #(4 * 8)]
> -	ldr	x8, [x3, #(3 * 8)]
> -	ldr	x7, [x3, #(2 * 8)]
> -	ldr	x6, [x3, #(1 * 8)]
> -	ldr	x5, [x3, #(0 * 8)]
> -
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> +	adr	x22, 1f
> +	add	x22, x22, x5, lsl #2
> +	br	x22
>  1:
> -	msr	dbgbcr15_el1, x20
> -	msr	dbgbcr14_el1, x19
> -	msr	dbgbcr13_el1, x18
> -	msr	dbgbcr12_el1, x17
> -	msr	dbgbcr11_el1, x16
> -	msr	dbgbcr10_el1, x15
> -	msr	dbgbcr9_el1, x14
> -	msr	dbgbcr8_el1, x13
> -	msr	dbgbcr7_el1, x12
> -	msr	dbgbcr6_el1, x11
> -	msr	dbgbcr5_el1, x10
> -	msr	dbgbcr4_el1, x9
> -	msr	dbgbcr3_el1, x8
> -	msr	dbgbcr2_el1, x7
> -	msr	dbgbcr1_el1, x6
> -	msr	dbgbcr0_el1, x5
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBVR0_EL1)
> -
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> +	ldr	x21, [x4, #(15 * 8)]
> +	ldr	x20, [x4, #(14 * 8)]
> +	ldr	x19, [x4, #(13 * 8)]
> +	ldr	x18, [x4, #(12 * 8)]
> +	ldr	x17, [x4, #(11 * 8)]
> +	ldr	x16, [x4, #(10 * 8)]
> +	ldr	x15, [x4, #(9 * 8)]
> +	ldr	x14, [x4, #(8 * 8)]
> +	ldr	x13, [x4, #(7 * 8)]
> +	ldr	x12, [x4, #(6 * 8)]
> +	ldr	x11, [x4, #(5 * 8)]
> +	ldr	x10, [x4, #(4 * 8)]
> +	ldr	x9, [x4, #(3 * 8)]
> +	ldr	x8, [x4, #(2 * 8)]
> +	ldr	x7, [x4, #(1 * 8)]
> +	ldr	x6, [x4, #(0 * 8)]
> +
> +	adr	x22, 1f
> +	add	x22, x22, x5, lsl #2
> +	br	x22
>  1:
> -	ldr	x20, [x3, #(15 * 8)]
> -	ldr	x19, [x3, #(14 * 8)]
> -	ldr	x18, [x3, #(13 * 8)]
> -	ldr	x17, [x3, #(12 * 8)]
> -	ldr	x16, [x3, #(11 * 8)]
> -	ldr	x15, [x3, #(10 * 8)]
> -	ldr	x14, [x3, #(9 * 8)]
> -	ldr	x13, [x3, #(8 * 8)]
> -	ldr	x12, [x3, #(7 * 8)]
> -	ldr	x11, [x3, #(6 * 8)]
> -	ldr	x10, [x3, #(5 * 8)]
> -	ldr	x9, [x3, #(4 * 8)]
> -	ldr	x8, [x3, #(3 * 8)]
> -	ldr	x7, [x3, #(2 * 8)]
> -	ldr	x6, [x3, #(1 * 8)]
> -	ldr	x5, [x3, #(0 * 8)]
> -
> -	adr	x26, 1f
> -	add	x26, x26, x24, lsl #2
> -	br	x26
> -1:
> -	msr	dbgbvr15_el1, x20
> -	msr	dbgbvr14_el1, x19
> -	msr	dbgbvr13_el1, x18
> -	msr	dbgbvr12_el1, x17
> -	msr	dbgbvr11_el1, x16
> -	msr	dbgbvr10_el1, x15
> -	msr	dbgbvr9_el1, x14
> -	msr	dbgbvr8_el1, x13
> -	msr	dbgbvr7_el1, x12
> -	msr	dbgbvr6_el1, x11
> -	msr	dbgbvr5_el1, x10
> -	msr	dbgbvr4_el1, x9
> -	msr	dbgbvr3_el1, x8
> -	msr	dbgbvr2_el1, x7
> -	msr	dbgbvr1_el1, x6
> -	msr	dbgbvr0_el1, x5
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGWCR0_EL1)
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -1:
> -	ldr	x20, [x3, #(15 * 8)]
> -	ldr	x19, [x3, #(14 * 8)]
> -	ldr	x18, [x3, #(13 * 8)]
> -	ldr	x17, [x3, #(12 * 8)]
> -	ldr	x16, [x3, #(11 * 8)]
> -	ldr	x15, [x3, #(10 * 8)]
> -	ldr	x14, [x3, #(9 * 8)]
> -	ldr	x13, [x3, #(8 * 8)]
> -	ldr	x12, [x3, #(7 * 8)]
> -	ldr	x11, [x3, #(6 * 8)]
> -	ldr	x10, [x3, #(5 * 8)]
> -	ldr	x9, [x3, #(4 * 8)]
> -	ldr	x8, [x3, #(3 * 8)]
> -	ldr	x7, [x3, #(2 * 8)]
> -	ldr	x6, [x3, #(1 * 8)]
> -	ldr	x5, [x3, #(0 * 8)]
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -1:
> -	msr	dbgwcr15_el1, x20
> -	msr	dbgwcr14_el1, x19
> -	msr	dbgwcr13_el1, x18
> -	msr	dbgwcr12_el1, x17
> -	msr	dbgwcr11_el1, x16
> -	msr	dbgwcr10_el1, x15
> -	msr	dbgwcr9_el1, x14
> -	msr	dbgwcr8_el1, x13
> -	msr	dbgwcr7_el1, x12
> -	msr	dbgwcr6_el1, x11
> -	msr	dbgwcr5_el1, x10
> -	msr	dbgwcr4_el1, x9
> -	msr	dbgwcr3_el1, x8
> -	msr	dbgwcr2_el1, x7
> -	msr	dbgwcr1_el1, x6
> -	msr	dbgwcr0_el1, x5
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGWVR0_EL1)
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -1:
> -	ldr	x20, [x3, #(15 * 8)]
> -	ldr	x19, [x3, #(14 * 8)]
> -	ldr	x18, [x3, #(13 * 8)]
> -	ldr	x17, [x3, #(12 * 8)]
> -	ldr	x16, [x3, #(11 * 8)]
> -	ldr	x15, [x3, #(10 * 8)]
> -	ldr	x14, [x3, #(9 * 8)]
> -	ldr	x13, [x3, #(8 * 8)]
> -	ldr	x12, [x3, #(7 * 8)]
> -	ldr	x11, [x3, #(6 * 8)]
> -	ldr	x10, [x3, #(5 * 8)]
> -	ldr	x9, [x3, #(4 * 8)]
> -	ldr	x8, [x3, #(3 * 8)]
> -	ldr	x7, [x3, #(2 * 8)]
> -	ldr	x6, [x3, #(1 * 8)]
> -	ldr	x5, [x3, #(0 * 8)]
> -
> -	adr	x26, 1f
> -	add	x26, x26, x25, lsl #2
> -	br	x26
> -1:
> -	msr	dbgwvr15_el1, x20
> -	msr	dbgwvr14_el1, x19
> -	msr	dbgwvr13_el1, x18
> -	msr	dbgwvr12_el1, x17
> -	msr	dbgwvr11_el1, x16
> -	msr	dbgwvr10_el1, x15
> -	msr	dbgwvr9_el1, x14
> -	msr	dbgwvr8_el1, x13
> -	msr	dbgwvr7_el1, x12
> -	msr	dbgwvr6_el1, x11
> -	msr	dbgwvr5_el1, x10
> -	msr	dbgwvr4_el1, x9
> -	msr	dbgwvr3_el1, x8
> -	msr	dbgwvr2_el1, x7
> -	msr	dbgwvr1_el1, x6
> -	msr	dbgwvr0_el1, x5
> -
> -	ldr	x21, [x2, #CPU_SYSREG_OFFSET(MDCCINT_EL1)]
> -	msr	mdccint_el1, x21
> +	msr	\type\()15_el1, x21
> +	msr	\type\()14_el1, x20
> +	msr	\type\()13_el1, x19
> +	msr	\type\()12_el1, x18
> +	msr	\type\()11_el1, x17
> +	msr	\type\()10_el1, x16
> +	msr	\type\()9_el1, x15
> +	msr	\type\()8_el1, x14
> +	msr	\type\()7_el1, x13
> +	msr	\type\()6_el1, x12
> +	msr	\type\()5_el1, x11
> +	msr	\type\()4_el1, x10
> +	msr	\type\()3_el1, x9
> +	msr	\type\()2_el1, x8
> +	msr	\type\()1_el1, x7
> +	msr	\type\()0_el1, x6
>  .endm
>  
>  .macro skip_32bit_state tmp, target
> @@ -887,12 +597,65 @@ __restore_sysregs:
>  	restore_sysregs
>  	ret
>  
> +/* Save debug state */
>  __save_debug:
> -	save_debug
> +	// x0: base address for vcpu context

why do we need the vcpu context here?

> +	// x2: ptr to current CPU context

what does 'current' mean here?

> +	// x3: ptr to debug registers
> +	// x4/x5: trashed

you're also trashing everything that save_debug_registers is...

> +
> +	mrs	x26, id_aa64dfr0_el1
> +	ubfx	x24, x26, #12, #4	// Extract BRPs
> +	ubfx	x25, x26, #20, #4	// Extract WRPs
> +	mov	w26, #15
> +	sub	w24, w26, w24		// How many BPs to skip
> +	sub	w25, w26, w25		// How many WPs to skip
> +
> +	mov     x5, x24
> +	add	x4, x3, #DEBUG_BCR
> +	save_debug_registers dbgbcr
> +	add	x4, x3, #DEBUG_BVR
> +	save_debug_registers dbgbvr
> +
> +	mov     x5, x25
> +	add	x4, x3, #DEBUG_WCR
> +	save_debug_registers dbgwcr
> +	add	x4, x3, #DEBUG_WVR
> +	save_debug_registers dbgwvr
> +
> +	mrs	x21, mdccint_el1
> +	str	x21, [x2, #CPU_SYSREG_OFFSET(MDCCINT_EL1)]
>  	ret
>  
> +/* Restore debug state */
>  __restore_debug:
> -	restore_debug
> +	// x0: base address for cpu context

same as above (also not here you say cpu context, above you say vcpu
context, this is confusing)

> +	// x2: ptr to current CPU context

same question with 'current' ?

> +	// x3: ptr to debug registers
> +	// x4/x5: trashed

same trash, you probably want to specify x4..x22 (note that you're
explicitly also touching x21 below).

> +
> +	mrs	x26, id_aa64dfr0_el1
> +	ubfx	x24, x26, #12, #4	// Extract BRPs
> +	ubfx	x25, x26, #20, #4	// Extract WRPs
> +	mov	w26, #15
> +	sub	w24, w26, w24		// How many BPs to skip
> +	sub	w25, w26, w25		// How many WPs to skip
> +
> +	mov     x5, x24
> +	add	x4, x3, #DEBUG_BCR
> +	setup_debug_registers dbgbcr
> +	add	x4, x3, #DEBUG_BVR
> +	setup_debug_registers dbgbvr
> +
> +	mov     x5, x25
> +	add	x4, x3, #DEBUG_WCR
> +	setup_debug_registers dbgwcr
> +	add	x4, x3, #DEBUG_WVR
> +	setup_debug_registers dbgwvr
> +
> +	ldr	x21, [x2, #CPU_SYSREG_OFFSET(MDCCINT_EL1)]
> +	msr	mdccint_el1, x21
> +
>  	ret
>  
>  __save_fpsimd:
> @@ -927,6 +690,7 @@ ENTRY(__kvm_vcpu_run)
>  	bl __save_sysregs
>  
>  	compute_debug_state 1f
> +	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
>  	bl	__save_debug
>  1:
>  	activate_traps
> @@ -942,6 +706,7 @@ ENTRY(__kvm_vcpu_run)
>  	bl __restore_fpsimd
>  
>  	skip_debug_state x3, 1f
> +	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)

why is this sysreg cpu offset the debug registers that you can apply
offsets of kvm_guest_debug_arch to?

>  	bl	__restore_debug
>  1:
>  	restore_guest_32bit_state
> @@ -962,6 +727,7 @@ __kvm_vcpu_return:
>  	bl __save_sysregs
>  
>  	skip_debug_state x3, 1f
> +	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
>  	bl	__save_debug
>  1:
>  	save_guest_32bit_state
> @@ -984,6 +750,7 @@ __kvm_vcpu_return:
>  	// already been saved. Note that we nuke the whole 64bit word.
>  	// If we ever add more flags, we'll have to be more careful...
>  	str	xzr, [x0, #VCPU_DEBUG_FLAGS]
> +	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
>  	bl	__restore_debug
>  1:
>  	restore_host_regs
> -- 
> 2.3.5
> 

Thanks,
-Christoffer